Depolarization Studies at COSY

Mitglied der Helmholtz-Gemeinschaft 

Antiproton Polarization Studies 

for FAIR 

How to produce polarized antiprotons (and what to use them for?) 

June 1, 2008 | Hans Ströher 

2nd VIQCD Mtg. (Ferrara, Italy)

Introduction 

~ 3 years ago, we proposed a 

method to polarize antiprotons 

by „spin-filtering“ 

1 giugno 2008 Institut für Kernphysik (IKP) Folie 2

Introduction 

New initiative, driven by the 

FAIR-project at GSI 


Introduction 

High Energy 

Storage Ring 

(HESR) 

for a beam of 

antiprotons 

(How) is it possible to provide 

polarized antiproton beams 

in HESR ? 


Plan of talk 

The (long) road to polarized antiprotons: 

Proposals, ideas, calculations, … 

Experiments 

Depolarization studies at COSY 

FILTEX (TSR) 

Spin-filtering at COSY 

Spin-filtering at AD/CERN 

Summary, Conclusion 

… taken on by the PAX-collaboration (Spokespersons: 

F. Rathmann (Jülich), P. Lenisa (Ferrara)) 


Proposed methods (1): Some history … 

Stern-Gerlach splitting never tried (huge effort) 

1 giugno 2008 Institut für Kernphysik (IKP) Folie 6 

EPAC 1988

Proposed methods (2): Recent paper 

Need for an experimental test of this idea ! 


Depolarization Studies at COSY: Idea 

• Use proton beam and co-moving electrons 

• Turn experiment around: p e p into p e p 

i.e. depolarization of a polarized proton beam 

COSY Velocity electron 

cooler mismatch 

(detuned) 


Depolarization Studies at COSY: Principle 

• Use (transversely) polarized proton beam circulating in COSY 

• Switch on (detuned) electron cooler to depolarize proton beam 

• Analyze proton polarization with internal D 2-cluster target of ANKE 

e-cooler 

p 

T p = 49 MeV 

ANKE cluster 

target & STT 


Depolarization Studies at COSY: Details 

Detuned Cooler 

Voltage 

T detuned = 50 s 

ΔV ~ 

few 100 V 

Nominal Cooler 

Voltage 

T nominal = 100 s 

D 2 target off 

Ecooler on/detuned 

D 2 target on 

Ecooler on 


Depolarization Studies at COSY: Measurements 

Beam current 


Depolarization Studies at COSY: Polarimetry 

pd elastic scattering; detection in 

silicon tracking telescopes (STT) 

p 

d 

Preliminary 


Depolarization Studies at COSY: Results 

σ depol = 

−ln P det uned 

P nominal 

Δt⋅d t⋅f rev 

!! Preliminary !! 

No effect observed, i.e. cross section must be 

many orders-of-magnitude smaller than 10 13 b ! 


v/c ~ 

0.002

Depolarization Studies at COSY: New calc´s 

No effect expected ! 

(NIM B) 

10.1016/JNIMB.2008.04.010 


~ 1 mb

Depolarization Studies at COSY: 

No effect expected, too ? 

(since high cross section is for longitudinal polarization) 

Note: disagreement w/ MSS calculation by 10 16 !! 


Spin-filtering: 

Polarization build-up of an originally unpolarized particle beam by 

repeated interaction with polarized hydrogen target, e.g. in a storage 

ring: 

Spin-filtering is known to work („FILTEX“); not clear, how (see above) 


Spin-filtering at TSR: „FILTEX“ 

TSR … Test Storage Ring at MPI Heidelberg 

FILTEX … Filter Experiment (1992) 


Spin-filtering at TSR: „FILTEX“ – proof-of-principle 

PhD of F. Rathmann 

Spin filtering works for protons 


Spin-filtering at COSY: Optimize, understand 

FILTEX 

Superconducting 

quadrupole 

(new) 

p 

p p = 0.3… GeV/c 


Need a „lowß 

section“ in 

COSY 

ABS + storage cell, 

Si-tracking det´s 

(HERMES)

Spin-filtering at COSY: Low-ß Section 

Beta functions [m] 

50 

45 

40 

35 

30 

25 

20 

15 

10 

5 

1 2 3 4 

0 

16.8 17.3 17.8 18.3 18.8 19.3 19.8 20.3 20.8 21.3 21.8 22.3 22.8 

Length [m] 

Need superconducting quadrupoles 

Target: Storage cell 

Polarimeter 


Spin-filtering at CERN/AD: pp and pd scattering 

• Target (equipment used, 

tested at COSY) 

• Electron cooler (upgrade 

of existing AD-cooler) 

• Snake (also longitudinal; 

new) 

Measurement of effective p polarization build-up cross section 

First measurement of spin-correlations in above reactions 


Spin-filtering at COSY: Milestones, timeline 

COSY: determine / optimize beam lifetime - needed for large 

filtering time (beamtime in II/2008) 

SC quadrupoles – design almost ready; companies have 

been contacted (order in 2008) 

COSY: set up HERMES-ABS and recoil detectors (2009) 

COSY: implement set-up in ring (early 2010), perform sf 

-measurements 

CERN/AD: LoI full proposal; move equipment and repeat 

with anti-protons (~ 2011) 

By 2012/13 we will know how to do spin-filtering!! 

Design the APR (antiproton polarizer ring) 


Hadron Physics „Dream Machine“ for FAIR: 

… an asymmetric (double-polarized) 

proton (15 GeV/c) – antiproton (3.5 GeV/c) collider 

using HESR, 

CSR and APR 


Quark Transversity Distribution in Drell-Yan: 

Double transverse spin asymmetry: 


Summary: 

p e − 

p e + 

long. trans. 

WAKBJ: gigantic ??? 

MSS: small small 

10 16 

p p 

p p 


Summary: 

p e − 

p e + 

long. trans. 



No depolarization of 

polarized protons 

p p 

p p 


Summary: 

p e − 

p e + 

long. trans. 



No depolarization of 

polarized protons 

p p 

p p 


Spin-filtering works: 

p (FILTEX) COSY 

p CERN/AD

Conclusion: 

The road towards polarized antiprotons is long … 

But: - clear roadmap 

- commitment by PAX-collaboration 

- first measurements/achievements 

We appreciate any help! 

Note: 

Now and here (expertise) 

or „never“ (not in a very long time)!

Depolarization Studies at COSY

Create successful ePaper yourself

Delete template?

Save as template?